The prototype of new LNA was the previous design made on IC MGA633P8 two years ago. The HPF and LPF filters previously were made on LC components and then been replaced to LFCN-1200 and HFCN-1200 filters from Mini-Circuts.
Fig. 1 LNA-23cm-SKY67151 schematic model
The project is a low noise amplifier range 23cm, made on the IC SKY67151 in the first stage. A distinctive feature of this LNA is MMIC and five dielectric resonators (BPF) between each stage. Also LNA has a high IP3 with very low value of NF.
The LNA designed in Microwave Office.
Fig. 2.1 Expected Gain plot
Fig. 2.2 Expected Noise figure plot
Fig. 2.3 Expected Stability plot
Fig. 2.4 Expected VSWR plot
The input VSWR is less than 1.5 and not achievable with the transistors in input stage. The chip contains embedded matching circuit which allows the smaller values of input VSWR. LNA is absolutely stable in the entire frequency range of the filter. BW at -3 dB equals 120MHz. The attenuation outside the passband is better than 40dB. Applying a filter of order 5 which coupled with high linearity LNA allows use in strong signals environment and other sources of RF interference.
The RF input power of 21dBm allows use the LNA with antenna relay which have very small separation between RX/TX ports in case of QRO. For low power transistors in other LNAs that power is rarely more than 5dBm.
The very low noise figure (NF < 0.3 dB) makes this LNA attractive for EME QSO. For convenience of use with different types of antenna relays there are available options with SMA and N-type input and output connectors. OIP3 LNA equals 37dBm.
Amplifier is built on SKY67151 and SPF5189 chips. The input matching circuit is designed to achieve the minimum NF with low ESR and high Q capacitors. The inductance is designed as a microstrip line and has the minimum loss (compared to SMD) which has a beneficial effect on the overall noise factor of the whole amplifier. Low-noise voltage regulator 6 Volt made on IC LP3878. Inductances in the power supply circuit are MPL. Power supply (+ 8V to +12V) of LNA can be fed through the cable or separate wire. There is also a protection against reverse polarity power supply.
Schematic circuit of LNA is shown on Pic. 3
Fig. 3 LNA-23cm-SKY67151 schematic circuit
The board size is 61 x 32 mm (FR4 material 1 mm with metallized holes)
Fig. 4 LNA-23cm-SKY67151 PCB
The housing is made following the microwave requirements by milling aluminum and coated with a composition for soldering.
The measurement results are shown in Pic. 5.1 and Pic. 5.2. The gain at 1296 MHz is about 36dB.
Bandwidth at -3 dB equals 124MHz. The attenuation outside the passband is better than 40dB.
Pic. 5.1 Amplitude-frequency response of LNA, BW=120MHz
The bandwidth of final version of LNA filter is 75MHz is -3 dB.
Pic. 5.2 Amplitude-frequency response of LNA, BW=75 MHz
Pic. 9 Amplitude-frequency response of LNA, BW=75 MHz
The graph of the noise figure (NF) is shown in Pic. 6
Pic. 6 NF of LNA
Technical specifications of the LNA-23cm-SKY67151
- Model: LNA-23cm-SKY67151
- Active elements: MMIC SKY67151, PGA-103+
- Gain: 35 dB
- Noise Figure: < 0.3 dB
- Output IP3: 37 dBm
- BW(-3 dB): 80 MHz
- P input: 21 dBm (max)
- DC voltage: 8 – 12 V
- DC current: 150 mA
- Impedance: 50 ohms
- RF connectors: N-female или SMA-female
- Dimensions: 110 mm x 43 mm x 20 mm (with connectors)
- Weight: 0.15 kg
The package contais